Motivation: While there are numerous programs that can predict RNA or DNA secondary structures, a program that predicts RNA/DNA hetero-dimers is still missing. The lack of easy to use tools for predicting their structure may be in part responsible for the small number of reports of biologically relevant RNA/DNA hetero-dimers. Results: We present here an extension to the widely used ViennaRNA Package [6] for the prediction of the structure of RNA/DNA hetero-dimers